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Can you check/adjust valves with the head off?

Discussion in 'XJ Technical Chat' started by anachronism, Apr 20, 2017.

  1. anachronism

    anachronism Member

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    1981 xj650.

    Exhaust studs on one cylinder broke, both flush with head. Then extractor broke off in one. After drilling that out, there wasn't anything left to tap, so shop brazed in a threaded tube to replace bolt hole. Lasted a year, pulled out yesterday. Choice is try rebrazing or give up on the head. The head is due for a valve adjustment.

    So, I am thinking next project is swapping on a new head. If I can adjust the valves of new head on the bench, two birds with one stone. Can I? Can't see a reason clearances would change. I have a line on a complete head so would be measuring with camshafts bolted in on the bench. Only difference I can see is no timing chain, can't see that affecting clearance measurement.

    Thanks!
     
  2. Alan63

    Alan63 Active Member

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    Yes, but if you do change a shim roll the cam around a couple times to seat the shim before double checking the measurements .
    Alan
     
  3. FJ111200

    FJ111200 Active Member

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    Be careful. One valve will always be open and so turning one cam without the other and you'll be looking at a collision of the valves. You have been warned.
     
  4. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    I'll recommend against that practice. You will need to build a fixture to hold the head so that there is absolutely no risk of an open valve coming in contact with the bench.
    Bent valves suck.
    The engine is a pre-built fixture for the head.
     
  5. anachronism

    anachronism Member

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    Ok, I am hearing that the measurements should be accurate, but actually spinning cams around off the bike is fraught.

    Measuring clearance involves a lot less jigging of the cams than actually replacing. I think I will make an attempt to measure and procure shims as needed. Cams need to come off to pull head anyways, so installing new shims would happen with cams off and head on the bike.

    Now I just have to figure out if I want to preemptively replace the exhaust studs on the new (used) head, risking breaking them off in the process, or to use the existing studs (risking breaking them off in the process).

    I love the bike, I hate the fasteners. Good lord.
     
  6. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    The trouble with the exhaust studs breaking comes from either over tightening the nuts, or not using anti-seize when installing the nuts. Cléan the threads, use anti-seize, torque to spec, and you're golden.
     
  7. Thrasher

    Thrasher Member

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    Using anti-seize may give you a false torque value.
     
  8. anachronism

    anachronism Member

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    I suspect 30 years of heat cycles makes them quite weak.

    How I broke 2 on one cylinder- Rode 20 miles into town. At some point, the nut rattled off onto the highway. Picked up a replacement nut in town, threaded it on and the stud twisted off before the nut had even pulled the pipe against the gasket/head.

    With no choices, rode home. On the way home the other stud broke off.

    At this point I trust tissue paper to be tougher than XJ exhaust studs.
     
  9. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    I will humbly disagree. The way you describe the method of failure is a sign of past abuse (by some prior owner).
    If it makes you more secure, go ahead and replace them. Be prepared for the possibility that some will shear off. The steel and aluminum have had plenty of time to become one (Yamaha didn't use anti-seize when installing the studs into the heads).
     
  10. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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  11. anachronism

    anachronism Member

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    So, the duh part about making sure the valves don't interfere is to loosen the camshaft caps on the other camshaft so that all valves are closed.

    Checked valves, found one in spec and 7 tight, which isn't a surprise at all. I'd have a heart attack if I bought a used head with a recent valvejob. Valves have been adjusted at least once because a few shims had number side up. Thank goodness they were (barely, in one case) readable.
     
  12. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    That is some kind of professional, attention-to-detail, PO wrenching right there.........
     
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  13. anachronism

    anachronism Member

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    After a weekend of wrenching, I got the heads swapped.

    I learned the following things.

    1. It is a lot easier to get the carbs off than I anticipated.
    2. The job itself is pretty straightforward and can be done in a day. It takes a lot more time when you have to backtrack/screw up.
    3. STUFF A RAG IN THE CAM CHAIN AREA AS SOON AS THE VALVE COVER COMES OFF. There is a ton of stuff you can drop in there. really easy to drop a Cam sprocket bolt, for one. I forgot to replace a rag after taking out the cams and then dropped a head cap nut in there. I then spent 3 hours alternating between peering down into the engine and telling myself a head nut couldn't have possibly made it past the cam chain and crank sprocket (seems tight when looking from above) and looking at the ground convinced it had to be there. Sure enough, when I finally decided to pull the oil pan, it was there.
    4. I am really happy you can pull the oil pan with the engine in the frame. Clearances aren't great, however, and it really sucks breaking loose 35 years of bonding between the tiny hex head and the pan/case. My fingers were hamburger after slamming the case HARD each time one finally unstuck. And yes, the nut was in there. Super happy it dropped all the way down.
    5. I wish the Haynes manual was more specific about the head dowels/rubber bits that make up the oil passages to the head. I torqued down the ebay head with only a rubber ring in one hole and a metal dowel in the other thinking these were the "dowels" mentioned- that is what the old head left in the cylinder block. Thankfully I noticed the "extras" in the gasket pack before I got past torquing the head. Unfortunately I still needed to take the head back off to correct.
    6. I wasted way too much time trying to time the cams. I was convinced there was too much slack between the two cams and kept trying to get them 1 tooth closer than what was correct timing. Correct timing does have a bit of slack that gets taken up by the center chain guide, the chain tensioner, and engine rotation.
    7. On the same note, it is easy to leave 1 tooth too much slack between the crank sprocket and the exhaust cam. When you rotate the engine to the C mark to tension, the exhaust cam should start spinning as soon as you spin the crank. If it takes a few degrees, you are a tooth or more too slack.
    8. You can only bolt in 1 bolt of the cam sprocket at a time because the other side is down in the head. You need to stick a bolt in to establish cam timing. The Haynes manual tells you to install bolts finger tight, and at least that I saw, NEVER TELLS YOU to install the other bolt (the one you can't until you rotate the engine, which you can't do until you are timed) AND NEVER TELLS YOU to torque them. I had the valve cover mostly reinstalled before I realized I hadn't tightened or installed 2 cam bolts. I had doubles for most bolts and other parts because I was swapping on a complete head. Thank god I didn't find out my mistake rolling down the highway...
    9. The Vesrah gasket set is the worst packaging ever. Gaskets were all stuck to the plastic wrap. The cylinder base gasket tore trying to get it seperated from the plastic, thankfully I didn't need that one.
    10. The Vesrah exhaust header gaskets were much thicker than stock. I had to precrush them to get enough threads on the exhaust studs to grab the nuts...
    11. Still amazed how painless getting the carbs back on, including the airbox boots. I thought that would be a lot harder than it turned out to be.
    12. Open initial startup, I had a prominent oil leak starting from the halfmoon on the exhaust side of the valvecover and going around the front to the cam chain. It was dripping oil down that corner of the head. The gasket looked correctly located and the bolts looked tightened correctly, so I decided to give it a day. Sure enough. I found no leaks after a 6 mile ride today. Gasket just needed time to swell a bit.

    My old head was in need of a valve adjustment (was planning on doing it just before the head broke). With the old head, the bike ran great and only had 14,000 miles.

    With the new head with freshly adjusted valves, I now get everyone saying that an XJ sounds like a sewing machine. The old head with (likely) tight valves never made that steady satisfying clack. With the new head, the bike is much more tolerant of choke settings when starting- the old head wanted choke just right and would be a lot balkier if you tried to pull down the choke too quickly.

    Power seems different too. On the new head it seems the bike has a little more low-end and more linear power. I'm used to the bike having a "step" around 3000 rpm and another around 7,000 where in a short RPM range the bike starts making lots more power, but those don't seem to be there anymore, replaced by a more gentle progressive surge the higher the RPM. I kind of liked it the other way. It never felt like a bog, just a little like on a 2 stroke when you hit the rpm range the exhaust is tuned for.

    My final musing is that the camshaft caps of my original head showed a lot of wear and scoring you could feel. Either the bike was over-revved while cold, run low on oil, or overheated. Cylinder bores looked good so I don't know, but the cam caps looked not good.
     
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  14. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Good write up, thanks for sharing this.
     
  15. Stumplifter

    Stumplifter Well-Known Member

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    Sounds like you learned ALOT. Now "we" know.
     

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